Laminated structural body

ABSTRACT

An object of the present invention is to provide a damping and soundproofing member not only excellent in an excellent damping and soundproofing effect but also excellent in easiness of forming thereof, especially capable of forming directly a damping and soundproofing layer on a substance to be adhered and further excellent in lightness, washing ability, durability, and the like. The invention relates to a structure formed by laminating cured product layers formed from plurality of fluid resin compositions on a substrate expecting a damping or soundproofing effect, wherein at least two cured product layers of the above cured product layers are different in hardness. Moreover, preferably, no part of the hardest layer in the above cured product layers is directly formed on the substrate and the hardest layer is formed on the substrate via an intermediate layer.

FIELD OF THE INVENTION

The present invention relates to a damping and soundproofing structurewherein laminated cured product layers of fluid resin compositions areformed on a substrate expecting a damping and soundproofing effect.Particularly, it relates to a damping and soundproofing structure to beused as a cover for devices such as information-recording devices,information-related devices, information-communicating devices, acousticdevices, and game-related devices for the purpose of damping vibrationand proofing sound.

BACKGROUND ART

Heretofore, since the information-recording devices such as HDD where adisk having recorded information is rotated possess moving parts, e.g.,a motor to rotate the disk and a head to read and write information onthe disk, vibration generated from themselves and vibration and soundleaked out of the devices through sympathetic vibration of the otherparts derived from the vibration of the moving parts become a bigproblem. With regard to the motor, a remarkable improvement in vibrationand sound has been achieved by changing a conventional bearing systeminto a fluid dynamic bearing but the improvement is not perfect.

Accordingly, an article like an aluminum tape, a metal plate made of,e.g., aluminum or stainless steel, a common vulcanized rubber sheet, orthe like is adhered as a damping material to the devices themselves withan adhesive or a double-faced adhesive tape. Moreover, vibration dampingbecomes an important problem in compact and lightweight devices, forexample, optical disks such as mini-disk and DVD, and compact videos.For solving such problems, there have been proposed a damping materialusing a specific thermoplastic material (JP-A-9-235477) and a dampingmaterial comprising a styrene-vinylisoprene-styrene block copolymer, athermoplastic material, and a softener (JP-A-10-204249).

With regard to the above damping and soundproofing materials, a dampingand soundproofing material having a desired shape is in principleobtained from a sheet-shape article by stamping out with a trimming die,but the trimming die is expensive, so that the cost of the damping andsoundproofing material becomes high as a natural consequence in the casethat the required number of the damping and soundproofing material issmall. In the case of precision devices, since a trouble may arise whenminute dusts invade inside the devices, individual parts are washedprior to their assembling. When the damping material is adhered with anadhesive or a double-faced adhesive tape, a member to which the dampingmaterial is adhered is washed in order to remove dusts attached at theadhesion process, but there arises a problem that detergent liquidpenetrates into the adhesive layer and some troubles may be causedlater. For avoiding this problem, the washing is sometimes not carriedout, but in that case, non-washing may also cause staining of theprecision devices.

Further, the use of a metal plate, especially stainless steel plate as adamping and soundproofing material is not adequate for the devices to belightweight owing to the weight. In the case of vulcanized rubbersheets, when the thickness is thinned for saving weight and size, thestrength of the sheets decreases and they are easy to be damaged at themolding, so that it is difficult to increase productivity. In addition,there is a fear that sulfur of a vulcanizing agent may remain and affectelectronic parts. Moreover, with regard to silicone rubbers, there is aproblem that staining of electrical contact points with a low molecularweight siloxane may be generate.

Furthermore, since the damping materials disclosed in JP-A-9-235477 andJP-A-10-204249 are necessarily molded thermally using an injectionmolding machine or the like, there is a problem similar to the case ofthe above rubber sheets that a damping layer should be formed beforehandand be bonded to a substance to be adhered when the damping layer cannotbe formed directly to the substance to be adhered depending on thematerial and shape of the substance to be adhered.

DISCLOSURE OF THE INVENTION

The present invention is made in view of the above problems and anobject thereof is to provide a damping and soundproofing member not onlyexcellent in a damping and soundproofing effect but also excellent ineasiness of forming thereof, especially capable of forming directly adamping and soundproofing layer to a substance to be adhered and furtherexcellent in lightness, washing ability, durability, and the like.

The object of the present invention set forth above has been achieved byproviding following laminated structure.

1. A laminated structure comprising: a substrate expecting a damping orsoundproofing effect; and laminated cured product layers formed fromplurality of fluid resin compositions provided on the substrate, whereinat least two of the cured product layers are different in hardness.

2. The laminated structure according to item 1, wherein the hardestlayer in the cured product layers has a hardness (JIS-D hardness) of 70or more.

3. The laminated structure according to item 1, wherein the hardestlayer in the cured product layers has a thickness of 10 μm or less.

4. The laminated structure according to item 1, wherein the softestlayer in the cured product layers has a hardness (JIS-A hardness) of 80or less.

5. The laminated structure according to item 1, wherein the softestlayer in the cured product layers has a thickness of 10 μm or more.

6. The laminated structure according to item 1, wherein no part of thehardest layer in the cured product layers is directly formed on thesubstrate.

7. The laminated structure according to item 6, wherein the hardestlayer in the above cured product layers is formed on the substrate viaan intermediate layer.

8. The laminated structure according to item 1, wherein the curedproduct layers are composed of two layers.

9. The laminated structure according to item 1, wherein the hardestlayer in the cured product layers has a specific gravity of 1.4 or more.

10. The laminated structure according to item 1, wherein the curedproduct layers are formed on at least part of the substrate.

11. The laminated structure according to item 1, wherein the substratehas concave part on its surface, and wherein the cured product layersare formed on the concave part of the substrate.

12. The laminated structure according to item 1, wherein the curedproduct layers are formed on at least one side of the substrate.

13. The laminated structure according to item 1, wherein the curedproduct layers comprise plurality of cured product layers different inglass transition temperature.

14. The laminated structure according to item 1, wherein the curedproduct layers are formed by applying and curing the fluid resincompositions.

15. The laminated structure according to item 1, wherein the curedproduct layers are sequentially formed by applying and curing therespective fluid resin composition.

16. The laminated structure according to item 1, wherein the substrateis a thin plate-shape having a thickness of 2 mm or less.

17. The laminated structure according to item 1, wherein the substrateis a cover part for an apparatus generating vibration and sound.

18. The laminated structure according to item 1, wherein the fluid resincompositions forming the cured product layers each has curabilityselected from the group consisting of energy beam curability, thermalcurability, moisture curability, and multi-liquid mixing curability.

19. The laminated structure according to item 1, wherein the fluid resincompositions forming the cured product layers each contains no tincompound.

20. The laminated structure according to item 1, wherein the fluid resincompositions forming the each cured product layers each contains no lowmolecular weight siloxane.

21. The laminated structure according to item 1, wherein the fluid resincompositions forming the cured product layers each has a total contentof anionic constituents of 100 ppm or less.

22. The laminated structure according to item 1, wherein the curedproduct layers each gives an outgas amount of 100 ppm or less.

Having the constitutions as described above, transmittance of vibrationand sound from original sources of vibration and sound can be inhibited.

BEST MODE FOR CARRYING OUT THE INVENTION

In the invention, the structure is formed by laminating cured productlayers forming from plurality of fluid resin compositions on a substrateexpecting damping or soundproofing effect, but individual cured productlayers to be formed may be any cured product layers different inhardness from each other. For example, the cured product layers maycomprise cured product layers of fluid resin compositions entirelydifferent in kind from each other or may comprise cured product layersof the same kind of fluid resin compositions by differentiatingindividual hardness of the cured product layers. The larger layer numberof the cured product layers to be laminated acts advantageously on adamping effect in many cases, but in consideration of actualprocessability, cost, damping and soundproofing properties, and thelike, preferable number of the laminated layers is one to five layers,and more preferable number of the laminated layers is two to threelayers. In this connection, it need scarcely be said that larger numberof the laminated layers is more preferable when damping andsoundproofing properties are pursued.

In the case that plurality of the cured product layers formed on asubstrate have a two-layer structure, layers having different hardness,i.e., a soft layer and a hard layer are to be laminated. For exhibitingbetter damping and soundproofing effect, it is preferable to form a softlayer and then a hard layer from a substrate side. Moreover, in the casethat the cured product layers have a structure having three or morelayers, it is sufficient that adjacent two layers are different inhardness from each other. For example, in the case of a three-layerstructure, the structure may have a cured product layer having adifferent hardness held tightly with two cured product layers having thesame hardness or three layers different in hardness from one another maybe laminated.

In this connection, the term “soft” or “hard” herein means relativehardness. In more preferred embodiments of the invention, the hardnessof a soft layer (the softest layer in the case of a structure havingthree or more layers) is 80 or less, more preferably 20 to 80, in termsof a value measured using a JIS-A hardness testing machine, and thehardness of a hard layer (the hardest layer in the case of a structurehaving three or more layers) is 70 or more, more preferably 70 to 100,in terms of a value measured using a JIS-D hardness testing machine.Even without the ranges, it is possible to exhibit an aimed damping andsoundproofing effect by thickening the cured product layers orincreasing the number of the laminated layers.

Furthermore, thicker cured product layer in the invention actsadvantageously on the damping and soundproofing effect in many cases,but in consideration of actual processability, cost, weight, size as afinal product, damping and soundproofing properties, and the like, thethickness of one cured product layer is 0.01 to 2 mm, preferably 0.1 to1 mm and the total thickness of the laminated layers is 0.1 to 3 mm,preferably 0.2 to 2 mm. The thickness of each layer constituting theplurality of layers may be the same or different.

Moreover, in the case that the cured product layers of fluid resincompositions formed on a substrate expecting a damping and soundproofingeffect is plurality of layers, the cured product layer(s) of fluid resincomposition(s) other than the cured product layer of a fluid resincomposition formed directly on a substrate expecting a damping andsoundproofing effect preferably do not come into direct contact with thesubstrate expecting a damping and soundproofing effect. Particularly, itis preferable that the hardest layer does not come into direct contactwith the substrate.

The hardness of each cured product layer in the invention is explainedto be relative one, but it can be expressed by using another parameter.In that case, a glass transition temperature of the cured product layeris used. For example, the expression that the glass transitiontemperature of the cured product layer forming a hard layer ispreferably higher than the glass transition temperature of the curedproduct layer forming a soft layer among cured product layers of fluidresin compositions used in the invention is possible. Specifically, theglass transition temperature of the cured product layer forming a softlayer is preferably −40 to 80° C. and that of the cured product layerforming a hard layer is preferably 70 to 150° C., and more preferably,the former is 0 to 70° C. and the latter is 80 to 140° C. In thisconnection, with regard to the temperature at which the glass transitiontemperature of the hard layer overlaps with that of the soft layer, whenthe glass transition temperature of the hard layer is 80° C., theproblem may be solved by setting the glass transition temperature of thesoft layer to a temperature lower than 80° C.

The fluid resin composition for use in the invention means a resincomposition having such a degree of flowability that mechanicalapplication by an applying apparatus, such as dispense application,screen printing, or transcription application is possible. In thissense, there is included a resin composition which is solid at roomtemperature but is softened upon heating to exhibit flowability, forexample, a hot-melt resin. Specific examples of the fluid resincomposition in the invention include various reactive resin compositionswhich are fluid at room temperature, solvent-evaporating type resincompositions wherein a thermoplastic resin is dissolved in solvent orwater, emulsion-type aqueous resin compositions, hot-melt-type resincompositions mentioned above, and the like. In this connection, thecured products of the fluid resin composition in the invention includethe cured products obtainable by reactive curing of reactive resincompositions, and in addition, solidified products obtainable by solventvaporization of solvent-evaporating type resin compositions oremulsion-type aqueous resin compositions, or solidified productsobtainable by cooling hot-melt resin compositions are also included inthe cured products in the invention.

Preferred examples of the above fluid resin composition include reactiveresin compositions which are liquid at room temperature, are capable offorming cured products easily within a short period, exhibit littleshrinkage at curing, and exert little influence on the environment fromthe viewpoint of easy handling. The reactive resin compositions includeacrylic resin compositions, epoxy resin compositions, urethane resincompositions, silicone resin compositions, modified siliconecompositions, and the like, but are not limited thereto. Moreover, asreactive curing mechanisms of the above reactive resin compositions, aphotoreaction, a thermal reaction, a reaction with moisture, an additionreaction, a condensation reaction, and the like are considered to bereaction modes, but in consideration of processability, it is preferableto have photopolymerizability, thermal polymerizability, or additionpolymerizability basically by radical polymerization or cationicpolymerization. More specific reactive resin compositions include(meth)acrylic ester resins, urethane(meth)acrylate resins,epoxy(meth)acrylate resins, urethane resins, one-component epoxy resins,two-component epoxy resins, and the like.

At the formation of individual cured product layers, as a reactive resincomposition forming a soft layer, an acrylic ester resin or a urethaneresin is preferably used and as a reactive resin composition forming ahard layer, an acrylic ester resin, an one-component epoxy resin, atwo-component epoxy resin and a urethane resin may be mentioned. In thisconnection, the fluid resin composition for use in the invention may bea solvent-evaporating type resin, but in view of processing, the resinis not so preferable since it requires an explosion-proof equipment. Inaddition, it is not preferable since outgas is generated from thesolvent component which has remained as a minute constituent.

In the case that an acrylic ester resin is used as the reactive resincomposition, it is preferable to prepare it as a photo-curable resincomposition from the viewpoint of its processability. Specifically, asthe photo-curable resin composition, a urethane acrylate or epoxyacrylate having a molecular weight Mw of 1000 to 10000 is used as anoligomer component, which is diluted with a (meth)acrylate monomer suchas 2-hydroxyethyl acrylate, or the like. As a polymerization initiator,a photo-initiator such as 2-hydroxyphenyl ketone (Ciba-Geigy, Irgacure#184) is added. In addition, various fillers such as silica, amorphoussilica, talc, and alumina can be also added thereto for the purpose ofimproving applicability or the like. Moreover, it is also possible toadd a silane coupling agent, a phosphate ester, or the like for thepurpose of improving adhesiveness to the substrate. This acrylic esterresin can be suitably used for the formation of a soft cured productlayer.

In the case that an epoxy resin is used as the reactive resincomposition, it is preferable to use an one-component epoxy resin fromthe viewpoint of its processability. The one-component epoxy resin ismainly composed of a reactive resin having an epoxy group and a potentcuring agent, and is reacted and cured upon heating. As the reactiveresin having an epoxy group, compounds having one or more epoxy groupsin one molecule can be used without limitation, and these compounds maybe used singly or as a mixture of two or more of them. Specific examplesof the reactive resin having an epoxy group include Epicoat 828 and 807(manufactured by Japan Epoxy Resin K.K.), Epiclon 803 and 835LV(manufactured by Dainippon Ink & Chemicals, Incorporated), and the like.As the potent curing agent which reacts with the reactive resin havingan epoxy group to cure it, dicyandiamine, FXE-1000 (manufactured by FujiKasei Kogyo Co., Ltd.), modified aliphatic amines, and the like. Inaddition, various fillers such as silica, amorphous silica, talc,alumina can be added thereto for the purpose of improving applicabilityor the like. Moreover, it is possible to add a silane coupling agent orthe like for the purpose of improving adhesiveness to the substrate. Inthe case that a cured product layer is formed using the epoxy resin, itis preferable to use the cured product layer as a hard cured productlayer. This is because a cured product of an epoxy resin generally tendsto afford a hard cured product and has a high glass transitiontemperature. When a filler having a high specific gravity, such as ametal powder, is further added thereto, a hard cured product having ahigh specific gravity is obtained, so that a cured product having a highdamping and soundproofing effect is easily obtained. In this connection,the hard cured product layer preferably has a specific gravity of 1.4 ormore, more preferably 1.8 or more, but it may vary depending on the kindof a reactive resin or a filler.

Furthermore, the fluid resin composition is preferably does not containany tin compound. Among tin compounds, organic tin compounds areespecially highly volatile and hence there is a fear that the compoundsmay invite malfunction of articles themselves produced using thecompounds, peripheral electronic parts and devices, and the like byre-attachment or transcript of outgas constituent from cured products.Actually, there arises a big problem in HDD. In the case that a urethane(meth)acrylate for example is used as the fluid resin composition, it ispreferable to use either an organic zinc or an amine compound withoutusing any tin compound as the synthetic catalyst which is disclosed inWO99/51653.

The cured product of the fluid resin composition preferably contains alesser outgas constituent and the content is preferably 100 ppm or less.This is because there is a fear that the outgas constituent may invitemalfunction of articles themselves produced using the constituent,peripheral electronic parts and devices, and the like. The content ofoutgas constituent is generally analyzed by GC (Gas Chromatograph) orGC/MS (Gas Chromatograph-Mass Spectrometer). Particularly, analysiscombined with DHS method (Dynamic Headspace Sampler method) is suitable.The conditions for extracting outgas constituent cannot be definedsweepingly, but the extraction conditions in the invention are definedas an extraction at 120° C. for 15 minutes.

Furthermore, the fluid resin composition preferably does not contain anylow molecular weight siloxane. This is because there is a fear that thelow molecular weight siloxane may invite malfunction of articlesthemselves produced using the siloxane, peripheral electronic parts anddevices, and the like.

The fluid resin composition of the invention preferably contains alesser content of total anionic constituents as its ionic constituent.Particularly, it is preferable for the composition that the totalcontent of F, Cl, Br, NO₂, NO₃, PO₄, and SO₄ ions is 100 ppm or less.This is because there is a fear that the anionic constituents may invitecorrosion or malfunction of articles themselves produced using theconstituents, peripheral electronic parts and devices, and the like. Thecontent of anionic constituents is generally analyzed by IC (IonChromatograph). The conditions for extracting anionic constituentscannot be defined sweepingly but the extraction conditions in theinvention are defined as an extraction at 80° C. for 1 hour usingpurified water.

Specific examples of the substrate expecting a damping and soundproofingeffect for use in the invention include home or in-car audio devices(cassette, CD, DVD, video, or AV devices carrying them, and accessorydevices such as speakers and microphone), information-related devices(various personal computers carrying HDD, CD-ROM, DVD, MO, and the like,game machines, and so on), information-communicating devices such asmobile phones, PHS (Personal Handyphone System), and pocket beeper, andalso cases and covers into which parts and apparatus, which is carriedby printers, copiers, and the like and generates vibration and sound,are mentioned.

In the invention, it is necessary to form cured products formed fromplurality of layers of fluid resin compositions on the above substrate.When the forming method is specifically explained, for example, thefirst fluid resin composition is applied on at least part of the surfaceof the substrate in a desired thickness and size and then the fluidresin composition is cured to form the first cured product layer. Then,the second fluid resin composition is applied on the above first curedproduct layer so as to be in the size equal or slightly smaller than thesize of the first cured product layer (the thickness is optional) andthe second cured product layer is formed to effect lamination so as toalmost lap over the first cured product layer. By forming the layers insuch a manner, the surface of the substrate can be strongly bonded tothe first cured product layer and also the first cured product layer tothe second cured product layer. At that time, it is extremely effectiveto form the second cured product layer so as not to come into directcontact with the surface of the substrate to achieve the object of theinvention since a damping and soundproofing effect can be furtherenhanced. Furthermore, the third cured product layer and the fourthcured product layer may be further formed in the same manner asdescribed above.

In an alternative method, a cured product A having a predetermined shapeand a predetermined thickness is formed beforehand, and then forlaminating this to the substrate, after the other fluid resincomposition is applied to the surface of the substrate, the above curedproduct A formed beforehand is placed thereon and then the above fluidresin composition is cured to laminate a cured product layer B and acured product layer A on the substrate.

The cured product layers to be formed and laminated on a thinplate-shape substrate may be formed any place on the substrate but, inorder to obtain more effective damping and soundproofing effect, it ispossible to form the layers on both front and back sides of thesubstrate. Moreover, the thin plate-shape substrate is molded in anappropriate thickness in order to reduce its weight and to facilitatebending processing. A thickness of the substrate is preferably 2 mm orless, for example, in the covering member of information recordingdevices, the thickness of the substrate is generally about 0.2 to 1.5mm, and in some case, there are slight concavity and convexity in thesurface so as to fit the member to the shape of a motor or electronicpart to be housed its inside. In such a case, when laminated curedproduct layers of fluid resin compositions are formed so as to fit themto the concave shape formed on the surface of the substrate, a beautifulfinish in appearance is afforded.

In the invention, it is advantageous and preferable to apply fluid resincompositions directly on the substrate successively to form curedproduct layers in view of processing, cost, and the like. Moreover, theapplying method of the fluid resin compositions may be any methodgenerally used. Specifically, screen printing, metal mask, sprayapplication, stamping application, dispenser application, and the likemay be mentioned. Dispenser application in combination with an automaticapplying robot is most preferable, which is flexibly responsible to theproperties, such as viscosity, of the fluid resin compositions and alsoto the change of shape of the substances to be applied (substrates) orwhich is advantageous in view of processing, cost, and the like.

EXAMPLES

The following will describe the invention with reference to Examples andComparative Examples but the invention is not limited to these Examples.

In Examples and Comparative Examples, a dispenser in combination with anautomatic applying robot was used at the application of fluid resincompositions on a substrate expecting a damping and soundproofingeffect. Desired cured product layers were formed by photo-curing with UVirradiation at curing the formulations forming soft layers and bythermal curing using a heating furnace at curing the formulationsforming hard layers. For evaluating the damping and soundproofingeffect, a commercially available HDD (2.5 inch, 40 G, 4200 rpm) waspurchased and, after forming the above cured product layers of fluidresin compositions in a predetermined thickness on the cover (about 70mm×95 mm), the evaluation was carried out by driving the HDD actually.The applied area of the fluid resin compositions was about 20 cm² forboth of soft layers and hard layers.

The following Formulations 1 and 2 were prepared as fluid resincompositions forming soft layers of a damping and soundproofingstructure and the following Formulations 3 and 4 were prepared as fluidresin compositions forming hard layers, respectively, to obtain reactiveresin compositions. At that time, all the individual raw materials usedfor preparation of the formulations were used after confirmingcontamination of no tin compound and no low molecular weight siloxane,and the preparation of the formulations were carried out carefully sothat the constituents were not mixed in from devices used for thepreparation of the formulations. When cured products of the preparedformulations were analyzed, the constituents were below detection limit.

The urethane acrylate for use in the following Formulations 1 and 2 wassynthesized as follows. First, 36 g of a polyether obtainable by addingpolypropylene ether to bisphenol A and having a hydroxy group at theterminal (trade name: Adeka Polyether BPX-11, manufactured by AsahiDenka K. K., molecular weight: about 360) was added to 50.05 g ofdiphenylmethane diisocyanate (MDI) in the presence of 0.04 g of zincoctylate of a reaction catalyst and an addition reaction was allowed tooccur at 60 to 80° C. to obtain a polyisocyanate oligomer having anisocyanate group at the terminal. One hundred grams of hydroxyethylacrylate which was equivalent to or more than the amount of theisocyanate group in the polyisocyanate oligomer was added to theoligomer and an addition reaction was allowed to occur at 60 to 80° C.in the presence of 0.04 g of zinc octylate as the reaction catalyst toobtain polyetherurethane acrylate having an acryl group at the terminal(Synthesis 1).

Formulation 1 (Photo-Curable Acrylic Resin Composition) Urethaneacrylate (Synthesis 1) 50 parts by weight Tetrahydrofurfuryl acrylate 50parts by weight Irgacure #184 (photo-initiator,  3 parts by weightmanufactured by Ciba Specialty Chemicals)

Physical properties and analytical results after photo-curing are asfollows:

-   -   JIS-A hardness: 50    -   Glass transition temperature: 10° C.    -   Content of outgas: 10 ppm    -   Content of total anionic constituents: 5 ppm

Formulation 2 (Photo-Curable Acrylic Resin Composition) Urethaneacrylate (Synthesis 1) 50 parts by weight Phenoxy acrylate 50 parts byweight Irgacure #184 (photo-initiator,  3 parts by weight manufacturedby Ciba Specialty Chemicals)

Physical properties and analytical results after photo-curing are asfollows:

-   -   JIS-A hardness: 40    -   Glass transition temperature: 0° C.    -   Content of outgas: 8 ppm    -   Content of total anionic constituents: 7 ppm

Formulation 3 (Thermally Curable Epoxy Resin Composition) Epicoat 828(Yuka Shell Epoxy K.K.) 100 parts by weight FXE-1000 (thermal curingagent, manufactured by  20 parts by weight Fuji Kasei Kogyo Co., Ltd.)AS-40 (alumina powder, manufactured by Showa 100 parts by weight DenkoK.K.)

Physical properties and analytical results after thermal curing are asfollows:

-   -   JIS-D hardness: 90    -   Glass transition temperature: 100° C.    -   Content of outgas: 1 ppm    -   Content of total anionic constituents: 30 ppm    -   Specific gravity: 1.8

Formulation 4 (Thermally Curable Epoxy Resin Composition) Epicoat 828(Yuka Shell Epoxy K.K.)  50 parts by weight Epicoat 807 (Yuka ShellEpoxy K.K.)  50 parts by weight FXE-1000 (thermal curing agent,manufactured by  20 parts by weight Fuji Kasei Kogyo Co., Ltd.) AS-40(alumina powder, manufactured by Showa) 100 parts by weight Denko K.K.

Physical properties and analytical results after thermal curing are asfollows:

-   -   JIS-D hardness: 90    -   Glass transition temperature: 95° C.    -   Content of outgas: 1 ppm    -   Content of total anionic constituents: 30 ppm    -   Specific gravity: 1.8

Comparative Examples 1 to 6

Each of Formulations 1 to 4 was applied on the outer surface of the HDDcover in a desired thickness (applied area was about 20 cm²) andsufficiently cured by light irradiation or heating to form a curedproduct layer, followed by its evaluation. The evaluation results wereshown in Table 1. The evaluation was carried out through relativecomparison with a blank cover on which no cured product layer wasformed, and its damping and soundproofing property was evaluated. Thecriteria for judgment were as follows.

-   AA: A remarkable damping and soundproofing effect is observed.-   A: A sufficient damping and soundproofing effect is observed.-   B: A damping and soundproofing effect is observed (practically    acceptable).-   C: A slight effect is observed, but practically unacceptable.

D: No or little damping and soundproofing effect is observed. TABLE 1Comparative Comparative Comparative Comparative Comparative ComparativeExample 1 Example 2 Example 3 Example 4 Example 5 Example 6 FormulationNo. 1 1 2 3 3 4 Thickness of cured 0.2 0.4 0.2 0.2 0.4 0.2 product (mm)Damping and C C C D C D sound-proofing effect

Examples 1 to 4

Each cured product layer was formed on the HDD cover in the order shownin Table 2. Formulation 1 or 2 was cured by UV irradiation after itsapplication and Formulation 3 or 4 was cured by heating after itsapplication. The thickness of the cured product layers of each layer was0.2 mm and the shape and area of the cured product layers were the sameas in Comparative Example 1. The second cured product layer was formedso as not to come into direct contact with the HDD cover. The evaluationresults were shown in Table 2. TABLE 2 Example 1 Example 2 Example 3Example 4 Formulation No. 1 1 2 2 of first layer Formulation No. 3 4 3 4of second layer Damping and A A AA AA Sound-proofing effectThe criteria for evaluating the damping and soundproofing effect are thesame as in Table 1.

Examples 5 to 6

Formulation 1 or 2 was applied on the HDD cover as the first curedproduct layer and cured, and Formulation 3 was applied thereon as thesecond cured product layer and cured. The thickness of the cured productlayers of each layer was 0.2 mm and the shape and area of the curedproduct layers were the same as in Comparative Example 1. Formulation 3forming the second cured product layer was applied so as to run overslightly from the first cured product layer and cured so as to come intodirect contact with the HDD cover. The evaluation results were shown inTable 3.

Examples 7 to 8

Formulations 3 and 4 were applied on the HDD cover as the first curedproduct layer and cured by heating, and Formulation 1 was appliedthereon as the second cured product layer and cured by UV irradiation.The thickness of the cured product layer of each layer was 0.2 mm andthe shape and area of the cured product layers were the same as inComparative Example 1. Formulation 1 of the above second cured productlayer was applied and cured so as not to come into direct contact withthe HDD cover. The evaluation results were shown in Table 3.

Examples 9 to 10

Each cured product layer was formed on the HDD cover in the order shownin Table 3. Formulation 1 or 2 was cured by UV irradiation after itsapplication and Formulation 3 or 4 was cured by heating after itsapplication. The thickness of the cured product layer of each layer was0.2 mm and the shape and area of the cured product layers were the sameas in Comparative Example 1. The second cured product layer and thefollowing layers were formed so as not to come into direct contact withthe HDD cover. The evaluation results were shown in Table 3. TABLE 3Example Example 5 Example 6 Example 7 Example 8 Example 9 10 FormulationNo. of 1 2 3 4 1 1 first layer Formulation No. of 3 3 1 1 2 3 secondlayer Formulation No. of — — — — 3 1 third layer Formulation No. of — —— — — 3 fourth layer Damping and B B B B AA*1 AA*1 Sound-proofing effectThe criteria for evaluating the damping and soundproofing effect are thesame as in Table 1.*1The damping and soundproofing effect was very high but the thicknessof the cured product layers increased and the weight increased.

From the results shown in Table 1, when even one layer of a soft curedproduct layer was formed on the surface of the substrate, a damping andsoundproofing effect was observed although the effect was only a little.It is proved that the damping and soundproofing effect is higher in thecase of a relatively soft cured product layer. Moreover, from Table 2,it is proved that the damping and soundproofing effect is higher in thecase that a soft cured product layer is first formed on the substrateand then a hard cured product layer is formed thereon. Especially, it isalso proved that the combination of cured product layers having a largedifference in hardness in proximity to each other is more effective.

From the results shown in Table 3, even in the case that the substrate,soft cured product layer(s), and hard cured product(s) are laminatedsuccessively, it is proved that the damping and soundproofing effect isadversely effected when part of the hard cured product layer is directlybonded to the substrate. Moreover, when the cured product layers arelaminated as three or more layers, the damping and soundproofing effectis enhanced but steps for the lamination increases and also the weightand thickness of the laminated cured product layers increase.

While the invention has been described in detail and with reference tospecific embodiments, it will be apparent to one skilled in the art thatvarious changes and modifications can be made therein without departingfrom the spirit and scope thereof.

The present application is based on Japanese Patent Application No.2002-341033 filed on Nov. 25, 2002, and the contents are incorporatedherein by reference.

INDUSTRIAL APPLICABILITY

According to the invention, a remarkable damping and soundproofingeffect is obtained by laminating at least two layers of cured productlayers different in hardness on the surface of a substrate requiringvibration-damping and soundproofing. Especially, the effect is enhancedby forming a hard cured product layer via a soft cured product layer onthe surface of the substrate and also by forming the hard cured productlayer so as not to come into direct contact with the substrate.Furthermore, larger difference in hardness between the soft curedproduct layer and the hard cured product layer tends to improve theeffect.

In addition, since fluid resin compositions are used for the formationof the cured product layers, it is possible to form the cured productlayers (damping and soundproofing layers) by applying the compositionson any place independent of the shape and size of the substrate(substance to be adhered), so that productivity is improved as comparedwith the method of adhering a sheet-shape vibration damping andsoundproofing material. Furthermore, since the bonding to the substrateor between the cured product layers is effected by curing the fluidcomposition(s), secure lamination is possible and detachment of thecured product layer(s) hardly occurs, so that change of the damping andsoundproofing effect with time is also little. Particularly, whenreactive resin compositions are selected as the fluid resincompositions, the formation of the cured product layers after theapplication on the substrate can be rapidly carried out, for example, byphoto-curing or thermal curing, so that productivity is remarkablyimproved.

Furthermore, when reactive resin compositions with little outgas oreluting ions are used as the cured products, the use of the compositionsin precision electronic parts such as HDD may not contaminate the partsand hence quality of the precision electronic parts can be improved to alarge extent.

1. A laminated structure comprising: a substrate expecting a damping orsoundproofing effect; and laminated cured product layers formed fromplurality of fluid resin compositions provided on the substrate, whereinat least two of the cured product layers are different in hardness. 2.The laminated structure according to claim 1, wherein the hardest layerin the cured product layers has a hardness (JIS-D hardness) of 70 ormore.
 3. The laminated structure according to claim 1, wherein thehardest layer in the cured product layers has a thickness of 10 μm ormore.
 4. The laminated structure according to claim 1, wherein thesoftest layer in the cured product layers has a hardness (JIS-Ahardness) of 80 or less.
 5. The laminated structure according to claim1, wherein the softest layer in the cured product layers has a thicknessof 10 μm or less.
 6. The laminated structure according to claim 1,wherein no part of the hardest layer in the cured product layers isdirectly formed on the substrate.
 7. The laminated structure accordingto claim 6, wherein the hardest layer in the above cured product layersis formed on the substrate via an intermediate layer.
 8. The laminatedstructure according to claim 1, wherein the cured product layers arecomposed of two layers.
 9. The laminated structure according to claim 1,wherein the hardest layer in the cured product layers has a specificgravity of 1.4 or more.
 10. The laminated structure according to claim1, wherein the cured product layers are formed on at least part of thesubstrate.
 11. The laminated structure according to claim 1, wherein thesubstrate has concave part on its surface, wherein the cured productlayers are formed on the concave part of the substrate.
 12. Thelaminated structure according to claim 1, wherein the cured productlayers are formed on at least one side of the substrate.
 13. Thelaminated structure according to claim 1, wherein the cured productlayers comprise plurality of cured product layers different in glasstransition temperature.
 14. The laminated structure according to claim1, wherein the cured product layers are formed by applying and curingthe fluid resin compositions.
 15. The laminated structure according toclaim 1, wherein the cured product layers are sequentially formed byapplying and curing the respective fluid resin composition.
 16. Thelaminated structure according to claim 1, wherein the substrate is athin plate-shape having a thickness of 2 mm or less.
 17. The laminatedstructure according to claim 1, wherein the substrate is a cover partfor an apparatus generating vibration and sound.
 18. The laminatedstructure according to claim 1, wherein the fluid resin compositionsforming the cured product layers each has curability selected from thegroup consisting of energy beam curability, thermal curability, moisturecurability, and multi-liquid mixing curability.
 19. The laminatedstructure according to claim 1, wherein the fluid resin compositionsforming the cured product layers each contains no tin compound.
 20. Thelaminated structure according to claim 1, wherein the fluid resincompositions forming the each cured product layers each contains no lowmolecular weight siloxane.
 21. The laminated structure according toclaim 1, wherein the fluid resin compositions forming the cured productlayers each has a total content of anionic constituents of 100 ppm orless.
 22. The laminated structure according to claim 1, wherein thecured product layers each gives an outgas amount of 100 ppm or less. 23.A damping or soundproofing method for a substrate by forming at leasttwo layers on at least one portion of the substrate, wherein the atleast two layers comprise: a first cured product layer disposed on thesubstrate, wherein the first cured product layer is formed from areactive fluid acrylic resin composition; and a second cured productlayer disposed on the first cured product layer, wherein the secondcured product layer is formed from a reactive fluid epoxy resincomposition.
 24. The damping or soundproofing method according to claim23, wherein the at least two layers are formed by a process comprising:forming the first cured product layer on the substrate; and forming thesecond cured product layer on the first cured product layer.
 25. Thedamping or soundproofing method according to claim 23, wherein the atleast two layers are formed by a process comprising: applying thereactive fluid acrylic resin composition on the substrate to form aapplied composition; disposing the second cured product layer on theapplied composition; and curing the applied composition to form thefirst cured product layer.
 26. The damping or soundproofing methodaccording to claim 23, wherein the first cured product layer is softerthan the second cured product layer.
 27. The damping or soundproofingmethod according to claim 23, wherein the reactive fluid acrylic resincomposition is a photo-curable acrylic resin composition.
 28. Thedamping or soundproofing method according to claim 23, wherein thereactive fluid acrylic resin composition comprises: a compositionincluding a resin selected from a group consisting of (meth)acrylicester resin, urethane (meth)acrylate resin and epoxy(meth)acrylateresin; and a photo-initiator.
 29. The damping or soundproofing methodaccording to claim 28, wherein the reactive fluid acrylic resincomposition further comprises a (meth)acrylate monomer.
 30. The dampingor soundproofing method according to claim 23, wherein the reactivefluid epoxy resin composition comprises: a reactive resin having anepoxy group; and a potent curing agent.
 31. The damping or soundproofingmethod according to claim 30, wherein the reactive fluid epoxy resincomposition further comprises a filler.
 32. The damping or soundproofingmethod according to claim 31, wherein the filler comprises a metalpowder.
 33. The damping or soundproofing method according to claim 23,wherein the second cured product layer has a hardness (JIS-D hardness)of 70 or more.
 34. The damping or soundproofing method according toclaim 23, wherein the second cured product layer has a thickness of 10μm or more.
 35. The damping or soundproofing method according to claim23, wherein the second cured product layer has a specific gravity of 1.4or more.
 36. The damping or soundproofing method according to claim 23,wherein the first cured product layer has a hardness (JIS-A hardness) of80 or less.
 37. The damping or soundproofing method according to claim23, wherein the first cured product layer has a thickness of 10 μm ormore.
 38. The damping or soundproofing method according to claim 23,wherein no part of the second cured product layer is directly formed onthe substrate.
 39. The damping or soundproofing method according toclaim 23, wherein the substrate has a concave part on its surface,wherein the at least two layers are formed on the concave part.
 40. Thedamping or soundproofing method according to claim 23, wherein the atleast two layers are formed on at least one surface of the substrate.41. The damping or soundproofing method according to claim 23, whereinthe at least two layers comprise plurality of cured product layersdifferent in glass transition temperature.
 42. The damping orsoundproofing method according to claim 23, wherein the at least twolayers are formed from fluid resin compositions each containing no tincompound.
 43. The damping or soundproofing method according to claim 23,wherein the at least two layers are formed from fluid resin compositionseach containing no low molecular weight siloxane.
 44. The damping orsoundproofing method according to claim 23, wherein the at least twolayers comprise cured product layers each gives an outgas amount of 100ppm or less.
 45. The damping or soundproofing method according to claim23, wherein the substrate is a cover part for a HDD.